Chloroplast division is driven by a macromolecular complex that assembles at the midplastid. The FtsZ ring (Z ring) is the central structure in this complex, and is composed of the functionally distinct cytoskeletal proteins FtsZ1 and FtsZ2. Recent studies in the heterologous Schizosaccharomyces pombe system showed that Arabidopsis FtsZ1 and FtsZ2 filaments have distinct assembly and turnover characteristics. To further analyze these FtsZs, we employed this system to compare the assembly and dynamic properties of FtsZ1 and FtsZ2 lacking their N- and/or C-termini with those of their full-length counterparts. Our data provide evidence that the N-terminus of FtsZ2 is critical for its structural dominance over FtsZ1, and that the N- and C-termini promote polymer bundling and turnover of both FtsZs and contribute to their distinct behaviors. We also assessed how ARC6 affects FtsZ2 filament dynamics, and found that it interacts with and stabilizes FtsZ2 filaments in S. pombe independent of its presumed Z-ring tethering function in planta. Finally, we generated FtsZ1-FtsZ2 coexpression constructs to facilitate reconstitution of more complex interaction networks. Our experiments yield new insight into factors influencing FtsZ behavior and highlight the utility of S. pombe for analyzing chloroplast FtsZs and their assembly regulators.

Replication of chloroplast in plant cells is an essential process that requires co-assembly of the tubulin-like plastid division proteins FtsZ1 and FtsZ2 at mid-chloroplast to form a ring structure called the Z-ring. The Z-ring is stabilized via its interaction with the transmembrane protein ARC6 on the inner envelope membrane of chloroplasts. Plants lacking ARC6 are defective in plastid division and contain only one or two enlarged chloroplasts per cell with abnormal localization of FtsZ: instead of a single Z-ring, many short FtsZ filaments are distributed throughout the chloroplast. ARC6 is thought to be the anchoring point for FtsZ assemblies. To investigate the role of ARC6 in FtsZ anchoring, the mobility of green fluorescent protein–tagged FtsZ assemblies was assessed by single particle tracking in mutant plants lacking the ARC6 protein. Mean square displacement analysis showed that the mobility of FtsZ assemblies is to a large extent characterized by anomalous diffusion behavior (indicative of intermittent binding) and restricted diffusion suggesting that besides ARC6-mediated anchoring, an additional FtsZ-anchoring mechanism is present in chloroplasts.